1. Field of the Invention
The present invention relates generally to a disk chucking mechanism, and more particularly, to a disk chucking mechanism that uses a magnet to attract a hub provided on a magnetic disk.
2. Description of the Related Art
The conventional floppy disk chucking mechanism has involved a metallic hub positioned at the center of a magnetic disk or other recording medium. FIG. 1, for example, shows an expanded view of the vicinity of a hub 102A of a lower grade or ordinary floppy disk 100A. As shown in the diagram, a hub 102A made of a magnetic metal, that is, a metal that is attracted by a magnet, is positioned in the center of the magnetic disk 103A. A roughly square chucking hole 104A is formed in a bottom portion 107 of the hub 102A. Additionally, a similarly roughly square positioning hole 105 is formed in the bottom portion 107 of the hub 102A at a position offset from the position of the chucking hole 104A.
FIG. 2A is a schematic diagram of a disk chucking mechanism 110 mounted on a conventional magnetic disk drive into which a lower grade or ordinary floppy disk 100 has been loaded. As shown in the diagram, the disk chucking mechanism 110 comprises a turntable 111, a spindle 112, a chuck magnet 114 and a drive pin 115.
The turntable 111 is supported by the spindle 112 via a supporting portion 113. The spindle 112 is constructed so as to be rotatably driven by a disk motor not shown in the diagram. The chuck magnet 114 is formed in the shape of a ring and positioned on top of the turntable 111 in such a way as to surround the supporting portion 113.
The drive pin 115 is positioned so as to correspond to the position at which the positioning hole 105 noted above is formed. This drive pin 115 is constructed so as to be movable in the Z1-Z2 direction depicted in the diagram by a leaf spring positioned at the bottom of the drive pin 115.
FIG. 2B shows a state in which the lower grade or ordinary floppy disk has been loaded into the disk chucking mechanism 110. At the time the lower grade or ordinary floppy disk 100A is loaded the hub 102A is attracted to the chuck magnet 114 and set upon the turntable 111. In such a state, it is sometimes the case that although the spindle 112 penetrates the chucking hole 104A the drive pin 115 does not penetrate the positioning hole 105. It should be noted that in this case the drive pin 115 moves in the Z2 direction due to the elastic deformation of the leaf spring 116.
If in the state described above the disk motor drives the turntable 111 via the spindle 112, then this rotation matches the positioning hole 105 to the drive pin 115 and the rotational force of the disk motor is then transmitted to the hub 102A.
That is, in the disk chucking mechanism 110 as described above, the rotational force of the disk motor is transmitted to the lower grade or ordinary floppy disk 100A via the drive pin 115 and, at the same time, serves both to position the hub 102A on top of the turntable 111 and to support the hub 102A. As a result, the attractive force of the chuck magnet 114 does not contribute to the rotating of the lower grade or ordinary floppy disk. Accordingly, the attractive force of the chuck magnet 114 should be relatively weak, that is, just enough so that the hub 102A does not separate from the turntable 111. Separately, an index signal is emitted at the lower grade or ordinary floppy disk drive in order to determine the starting point of the disk that rotates in tandem with the position of the drive pin 115.
However, ever-larger capacity floppy disks and magnetic disk drives using these large-capacity floppy disks to magnetically record and reproduce have been and continue to be developed for the lower grade or ordinary floppy disk 100A and magnetic disk drive noted above. With the higher grade or high-density floppy disk drive the load that the magnetic head imparts to the rotation of the disk is small and moreover the load that the protective liner inside the disk cartridge imparts to the disk is set so as to be low, so there is no expectation of accurate positioning and support by the drive pin 115. Further, there is no emission of an index signal linked to the drive pin 115.
As a result, as shown by the expanded view depicted in FIG. 3 a circular chucking hole 104B is provided on a central portion 108 of the hub 102B of the higher grade or high-density floppy disk 100B and, at the same time, a peripheral portion of the hub 102B is formed into a ring-like projection 106. Unlike the lower grade or ordinary floppy disk 100A, the load torque on the rotation of the higher grade or high-density floppy disk 100B decreases and therefore the spindle 112 and the drive pin 115 cannot be expected to support the hub 102B, with the result that the positioned state is maintained only by the friction between the hub 102A and the turntable 111.
However, a so-called compatible magnetic disk drive has been proposed that makes it possible to magnetically record and reproduce on both the lower grade or ordinary floppy disk 100A and the higher grade or high-density floppy disk 100B using a single floppy disk drive. The compatible disk drive makes it possible to use the conventional lower grade or ordinary floppy disk 100A as is.
Conventionally, the disk chucking mechanism mounted on the compatible disk drive is the same disk chucking mechanism 110 mounted on the lower grade or ordinary floppy disk drive described above.
FIG. 2C shows a state in which the higher grade or high-density floppy disk 100B is loaded into the disk chucking mechanism 110. When loading, the center portion 108 of the hub 102B provided on the higher grade or high-density floppy disk 100B is attracted to the chuck magnet 114 and set on top of the turntable 111. In this condition, the spindle 112 enters the chucking hole 104B.
However, when the lower grade or ordinary floppy disk drive disk chucking mechanism is used as the disk changing mechanism of the convertible disk drive, the position of the floppy disk on top of the turntable 111 fluctuates due to external vibrations.
Increasing the strength of the chuck magnet 114 is one possible method of eliminating these fluctuations. In so doing, however, the great strength of the chuck magnet 114 causes the hub 102A of the lower grade or ordinary floppy disk 100A to stop where it lands on top of the turntable 111, the hub 102A does not rotate on top of the turntable 111 and, accordingly, the drive pin 115 may not enter the positioning hole 105.